Recently, various studies have shown that silicon fine particles, i.e., so-called nanosilicons, have unique characteristics which cannot be achieved by silicon crystal. The most typical characteristic is a light-emitting characteristic. The nanosilicons, which have the light-emitting characteristic but are made of an environmentally-friendly material, have been attracting attention as an environmentally-friendly light-emitting material. In light emission of the nanosilicons, a size effect of silicon particles is essential. That is, the nanosilicons emit light when radiative recombination of electrons and electron holes is caused by excitation. Well-known light emission modes involving the excitation are the following four modes: photoluminescence induced by photoexcitation, cathodoluminescence induced by electron beam irradiation to a substance, electroluminescence induced by a directly-injected electrical current, and thermoluminescence induced by heat.
As for a photoluminescence element, for example, Patent Literature 1 discloses a technique which makes use of a light-emitting characteristic of the silicone fine particles themselves. According to the technique, a light-emitting element is made in such a manner that (i) silicon fine particles in a form of three-dimensional web are obtained by irradiating a silicon target with a laser and then (ii) the silicon fine particles are encapsulated into thermosetting silicon. The silicon fine particles in the form of three-dimensional web were found to emit blue light of 467 nm when being subjected to 300-nm excitation light under a 77 K environment.
Further, for example, Patent Literature 2 discloses a technique of obtaining white light by modifying, with an organic matter, a surface of each of the silicon fine particles so as to broaden a photoluminescence spectrum. According to the technique, a light emitting element is obtained by modifying, with a hydrocarbon group, the surface of each of the silicon fine particles so as to shape the each of the silicon fine particles into a pellet form. Such a light emitting element emits white light in response to excitation light, which is emitted by an ultraviolet LED serving as an excitation light source.
As for an electroluminescence element or a cathodoluminescence element, for example, Patent Literature 3 discloses a light emitting element employing nanosilicons which are obtained by anodizing crystal silicon. According to this light emitting element, light of any wavelength, from infrared light to ultraviolet light, is emitted in such a manner that hot electrons (ballistic electrons), which serve as carriers and are obtained in an electron drift layer including nanosilicons, excite a light emitting layer (electron drift layer) made by depositing the nanosilicons. Further, for example, Patent Literature 4 discloses a method of producing a light emitting element, which employs similar nanosilicons as above, by carrying out a high-frequency sputtering method in combination with an annealing treatment. According to the techniques of Patent Literatures 3 and 4, a size of each of the nanosilicon fine particles is an important factor for achieving multicolor light emission. That is, the light emitted turns red, green, and/or blue, i.e., three primary colors of light, depending on the size of each of the nanosilicon fine particles.
Further, for example, Patent Literature 5 discloses a display device employing a cathodoluminescence element.